Appleton Tracy & Co-The early days of what was to become the Waltham Watch Company were marked financial failures and reorganizations.  One of the reorganized companies was names Appleton Tracy and Company.  Waltham kept the name and used it as an indication of grade. 
Crescent Street-The Waltham Factory was located on Crescent Street in Waltham Massachusets.  Waltham used the name as an indication of grade.  It is the second highest grade of regular production watches made by Waltham and was accepted into railway service.  It was origianlly used on the Model 1870 which has the destinction of being the first watch advertised as a "Railroad" Watch. 

Grade 845-A 21 Jewel movement first seen in the 12 million range which becomes the predominant 21 Jewel movement in the 14 millions and remains so until the end of Model 92 production.

Gray Book-In 1954 Waltham published a serial number list as an aid to watchmakers when ordering parts.  It is commonly referred to by collectors as the "Gray Book" because of the color of its cover.  It states on the first page that different grades of any given model were lumped together so it is not of much use in determining production figures.
Isochronism-When used in watchmaking, refers to the adjustment made to compensate for the difference in power as the mainspring is winding down.  This is acheived by bending the outermost coil of the hairspring up and then in over the main body of the hairspring.  It is referred to as the overcoil.  The word comes from the Greek iso meaning the same and chron meaning time. 
P.S. Bartlett-An early memeber of the Waltham organization whose name was used as an indication of grade on many Waltham models.  On Model 92s, it is always a 2-tone movement.
Vanguard-The original name of the Model 1892.  It represents the highest grade of regular production movements made by Waltham and was accepted into railroad service.  In the Model 92 it was made in 17, 19, 21 and 23 jewel movements.  The name is also found on 16 size Walthams.
Subpages (1): Case Screw Location